Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of integrated circuit devices. Generally, in these processes, a coated film of a photoresist composition is applied to a substrate such as silicon wafers used for making integrated circuits, circuit boards and flat panel display substrates. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to actinic radiation.
This actinic radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, extreme ultraviolet (EUV), electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed areas (for positive-type photoresists) or the unexposed areas (for negative-type photoresists) of the coated surface of the substrate.
After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution, plasma gases or reactive ions, or have metal or metal composites deposited in the spaces of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a patterned substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase its adhesion to the underlying substrate.
In the manufacture of patterned structures, such as wafer level packaging, displays, light emitting diode applications or microelectromechanical systems, electrochemical deposition of electrical interconnects has been used as the interconnect density increases. For example, see Solomon, Electrochemically Deposited Solder Bumps for Wafer-Level Packaging, Packaging/Assembly, Solid State Technology, pages 84-88, April 2001. Gold bumps, copper or other metal posts and copper traces for redistribution in wafer level packaging require a photoresist mold that can later be electroplated to form the final metal structures in advanced interconnect technologies. The photoresist layers are very thick compared to the photoresists used in the IC manufacturing of critical layers. Both feature size and photoresist thickness are typically in the range of 2 μm to 100 μm, (micrometers) so that high aspect ratios (photoresist thickness to line size) have to be patterned in the photoresist.
Positive-acting photoresists comprising novolak polymers and quinone-diazide compounds as photoactive compounds are well known in the art. Novolak polymers may also be reacted with quinone diazides and combined with a polymer. It has been found that photoresists based on only novolak/diazide do not have the photosensitivity or the steepness of sidewalls necessary for certain type of processes, especially for very thick films. Moreover a high dark-film loss in the developer is often observed.
Known chemically amplified photoresists, such as those based on blocked poly-4-hydroxystyrene (PHOST), blocked copolymers comprising hydroxystyrene and a blocked (meth)acrylic acid repeat unit such as tert-butyl(meth)acrylate, or (meth)acrylic materials comprising alicyclic groups, acid cleavable groups, and dissolution modifying groups such as anhydrides or lactones may exhibit the required photosensitivity but may also exhibit adhesion failure, during subsequent unit operations such as plating or etching. Such failures may lead to feature sidewalls that are rough, undercut or have protrusions somewhere in the metal feature. Moreover, these photoresists may be prohibitively expensive.
Therefore, there remains a need for a positive photoresist material that exhibits high photosensitivity, even in thick film applications, requires process worthy development times, exhibits low dark film loss in developers and basic plating solutions, and withstands wet plating and etching operations to produce features that have smooth side walls. The present disclosure and the accompanying claims address these needs.